Method and device for gauging magnetic materials



C. H. ANGELL April ll, 1950 METHOD AND DEVICE FOR GAUGING IAGNETIC IATERIALS Filed March 17, 1945 IN VEN TOR.

3 m H w L m H c B mae; Apr. 1950 &503.721

METHOD AND DEVI MAGNETIC Charles H. Angell, Danv uel C. Hu-ley, Jr., Hurley,

CE FOR GAUGING MATERIALS ille, Ill., assignor to Sam- Danville, Ill.: Wilmina L. executrix of said Samuel C. Harley, Jr.,

deceased, assignor to Wilmina L. Harley, Danvllle, Ill.

Application March 17, 1945, Serial No. .583,341

1 Claim. l

This invention relates to methods and apparatus for gauging magnetic materials and particularly for gaugingthe thickness of sheet material. A broad aspect of my invention comprises an improved method and apparatus for gauging the thickness of a magnetic material using the principlecf the electromagnet wherein the fiux resulting from variations in the width of the air gap due to variations in the thickness of the material gauged is used as a means to measure, indicate or control the thickness, which to my knowledge has never been done before. The gauging may be accomplished by either direct measurement, indirect measurement, gauging against a standard of thickness comparison, and other specific gauging procedures.

One object of my invention is to provide a novel method and apparatus for the continuous indication of the thickness of sheet material wherein the thickness of the material must be controlled within a definite tolerance range.

A further object of my invention is to provide a novel method and apparatus useful in Sorting metal sheets according to thickness.

A more specific object of my invention is to provide a novel means in the electromagnetic gauging of magnetic materials wherein vibrations in the supporting base and in the material being gauged do not affect the results of the gauging to a substantial extent.

Another specific object of my invention is to provide a method and apparatus in the gauging of magnetic materials for obtaining direct readings in dimensional terms for which no Satisfactory method and apparatus has heretofore been provided.

A broad embodiment of my invention comprises the use of at least two opposing electromagnets spaced apart and positioned as to form a space between the poles of the two magnets with means for positioning the material to be gauged by the electromagnets in said space.

Another important object in my invention is to provide a method and apparatus wherein the apparatus need only be calibrated once and does not need repeated calibrations for each standard of thickness comparison.

A more specific object of my invention for gauging magnetic materials is to provide an improved method and apparatus for obtaining the zero or starting point from which variations of flux due to variations in width of the air gap are measured.

Another important aspect of my invention is to provide a gauging device employing electromagnetic principles having an inductance coil associated with each gauging magnet and positioning the inductance coils in a novel manner in an impedance bridge circuit to which is connected a source of alternating current and a current responsive means such that the sensitivity of the gauging device is increased. By sensitivity is meant the ratio of the amperes of current resulting from the flux flowing through the air gap to the width of the air gap. The air gap is the distance between the gauging magnets and the material being gauged. In my invention, the magnetic material being gauged acts as a gauging shunt or armature for the provision of the path for the lines of fiux to travel. The greater the current fiowing through the current responsive means for a given width oi air gap or given thickless of material measured, the more sensitive and the more accurate is the gauging device.

A broad embodiment of my invention comprises the use of at least two opposing electromagnets spaced apart and positioned as to form an air gap between the poles of the two magnets with means for positioning the material to be gauged between the electromagnets in the air gap. By passing undirectional lines of fiux from the electromagnets to the material being gauged, a means is provided for indicating the thickness of the material independent of the exact position of the material in the air gap which is an extremely important feature of my invention since it is usually difficult, if not impossible, to accurately position the material to be gauged in the air gap or to avoid vibrations in the supporting base. In my invention such vibrations or accuracy in the positioning are immaterial since the current responsive means associated with the device 'measures the actual decrease in the air gap between the two electromagnets independent of such outside influences. The only thing that must be avoided is the actual touching of the material to be gauged by any of the poles of the electromagnets.

various means for obtaining the thickness measurement in terms of fiux or for comparing the thickness of the sheet material against a standard of thickness comparison may be used. I prefer to use a device wherein the variations of flux due to the variations in the thickness of the air gap caused by variations in the thickness of the material are always the same regardless of the standard of thickness comparison; or, in other words, it is independent of the standard of thickness comparison thereby providing the same sensitivity regardless of the thickness oi' the material to be gauged.

I accompilsh this object by always obtaining the same predetermined air gap regardless ot the standard of thickness comparison and thus variations in the air gap due to changes in the thickness of the material necessarily result in the same change in the amount of flux. For example, in the gauging of sheet magnetic materials, a. predetermined air gap is selected equal to the largest thickness of material to be gauged and the resulting current from the flux flowing between the two opposed magnets is measured and the current responsive means is set at the zero point. The standard of thickness comparison is then placed in the air gap which in effect narrows the air gap because the material acts as a shunt between the two electromagnets. The relative position of the electromagnets of my device are then adjusted so that the total air gap between each of the magnets and the standard of thickness comparison is equal to the prevlously determined air ga for the standard of thickness comparison, or in other words, until the same zero reading is obtained. The instrument is now ready for gauging and the material to be gauged is placed in the air gap between the two electromagnets and the variations in flux, as indicated by the current responsive means compared with the zero reading or the flux obtained for' the standard of thickness comparison, is used as an indication of the thickness of the material gauged. It is also readily seen that direct measurements may be obtained by placing the material to be gauged in the device and measuring by any well-known means, such as a ring gauge, the extent of the adjustment required to obtain the same zero point as for the standard of thickness comparison.

Another method and device I may use, although it is not to be 'considered equivalent, is the arranging of the two electromagnets as above described in a novel manner in an impedance bridge circuit, wherein the inductance coils associated with each of the magnets for the gauging device and associated with each of the magnets for a standard of thickness comparison device are-respectively arranged in diagonally opposed arms oi the bridge, and the flux resulting from changes in thickness of the material gauged s directly compared with the flux resulting from the standard of thickness comparison positioned in the standard of thickness comparison device.

These methods will become more readily apparent by referring to the drawings in which:

Fig. 1 shows the means for positioning the two electromagnets with provision for the air gap and means for positiom'ng the material to be gauged in the air gap. Fig. 1 is only illustrative and any other device within the teaching of my invention may be used.

Fig. 2 shows an impedance bridge circuit having the inductance coils associated with the gauging magnets positioned in the opposite arms of the bridge. It also illustrates a current responsive means for determining the magnitude of the flux. r

Fig. 3 is similar to Fig. 2 with the exception that the inductance coils associated with the gauging magnets are positioned in parallel in one arm of the bridge.

Fig. 4 is a simplified illustrative drawing showing the use of a standard of thickness comparison gauging magnet for obtaining a comparison with the material to be gauged in the gauging magnets.

Helen-ing to Fig. 1, a !rame I tor the electromagnets and tor posltioning the material to be gauged is provided. The !rame may be attached to a larger positioning frame by any means not shown in any suitable manner. A pair of gauging magnets 2 and 3, oppositely disposed on each side of the material to be gauged 4, are provided. A yoke 5 for attaching the two poles G and 'l oi magnet 2 and a yoke 8 i'or attaching the two poles 9 and o of magnet 3 are provided. Insulators II are provided for each of the magnets to prevent the short circuiting of the lines ot flux through the yoke. An inductance coil z around the core !3 is associated with magnet 2. and an inductance coil l4 associated with core IE is provided for magnet 3. These coils are connected to a source of alternating current and also to a current responsive means, as will be described later in connection with Fig. 2. Withln the scope of my invention, means may be provided for adjusting the distance between the poles the two opposed electromagnets. While any means within the scope of my invention may be used, I provide a shaft 16 attached to the yoke 5 of magnet 2 which extends through the frame I, and the up-and-down movement of the magnet 2- is adjusted by means of the adjusting nut I'I threaded to the pole IE and bearing on the upper frame as shown. A spring l8 is provided between the frame l and the yoke 5 to provide sufilcient tension for flrmiy holding the magnet in proper position for gauging.

The material to be gauged 4 is positioned in the device or passed through the air gap by means of fixed rollers s journaled in the frame, as shown, and movable rollers 20 journaled in the U-shaped elements 2l. Shafts 22 are fixedly attached to the elements 2l and are journaled in the upper portion of the irame l as indicated. Springs 23 provide suitable tension for flrmly holding the material to be gauged 4 in place.

Fig. 2 shows one method and means of interpreting the results of the gaugng operation. An impedance bridge circuit employing a suitable current responsive means is provided for determining the variation in the flux. Other arrangements may be used, including telemeters, recorders, relays, automatic thickness controlling apparatus and the like. The impedance bridge circuit contains reactance coils |2 and !4, which are the reactance or inductance coils described in Fig. 1, as being 'associated with electromagnets 2 and 3, respectively. Reactance coils 24 and 25 are provided for balancing the bridge circuit. The bridge circuit is connected to a source of alternating current shown at 26. A connection is made across the bridge circuit including a copper oxide rectifier 21 which is a well-known type of rectifying means to change the alternating current into direct current, although other types of suitable rectifiers may be used. A current responsive means such as the milliammeter 21' is provided to measure the current fiowing across the bridge circuit when the bridge is unbalanced. When the bridge is in balance, no current will flow across the bridge and the needle 28 is at the zero point as indicated and any change in flux created by the electromagnets will cause an unbalance in the arms of the bridge in which are connected the inductance coils |2 and I4, and the needle will be deflected and will indicate the extent of such change in flux, thus providing a means for indicating the thickness of the material.

Fig. 3 is similar to Fig. 2 with the exoeption that the inductance coils |2 'and I I are positioned in parallel in one arm of the bridge and a standard impedance coil 35 is positioned in the diagonally disposed arm of the bridge in order to balance the bridge circuit. This circuit is particularly adaptable for measurements wherein a constant ai: gap is maintained independent of the thickness of the standard of comparison. Furthermore, this circuit has the advantage that any vibrations in the device for positioning the material during gauging does not aflect the results appreciable, since by arranging coils |2 and ll in parallel in one arm of the bridge such changes in flux due to the vibrations oil-set each other and thereby the amount of current indicated by the milliammeter 21' is not afiected except by the change in the thickness of the material.

A typical operation of the device described and illustrated for Figs. 1 and 3 is as follows: If it is desired to measure materials less than inch thick, the distance between the poles of the magnets 2 and 3, without any material to be gauged disposed therebetween, is adjusted by means of the adjusting nut l'l until an air gap of /2 inch is obtained. The needle 28 of the instrument 21 is then set at the zero point. Assuming it is desired to compare the thickness of the material gauged against a standard of thickness comparison equal to /4 inch, such standard of thickness comparison is placed in the air gap as shown in Fig. 1 by the numeral 4, and the magnet 2 by means of adjusting nut Il is raised until the needle 28 again reaches the zero point which means the same air gap is obtained for a standard of thicknesses comparison of /2 inch as tor the previously determined air, gap. The standard of thickness comparison is now removed from the device and the material is ready for ge -181Z 8- The material to be gauged is now placed in the device and any variation of thickness from the standard of thickness comparison causes a change of flux difrering from the ilux resulting when the standard of thickness comparison was in the device. and variations in flux will be indicated in milliamperes by the needle 28 of the instrument 21. By always obtaining the same air gap tor each standard of thickness comparison, it is obvious that the same sensitivity is always obtained and it also provides a simple way of obtaining the zero point from which all measurements are made.

A typical operation using the apparatus shown in Flgs. 1 and 2 is as follows:

A standard o! thickness comparison is placed in position in the apparatus of Fig. 1 and the gauging magnet I: is adjusted until the zero point of milliammeter 21' is obtained. The standard oi' thickness comparison is now removed and the material to be gauged is placed in the apparatus and any variation in thickness from the standard o! thickness comparison will be reflected in millimeters by the instrument 21'.

In Flg. 4, 29 shows the thickness gauging device of Flg. 1 using magnets 2 and 3 in simplified form. It is understood that suitable means similar to that shown in Flg. 1 must be used to provide a complete workable apparatus. Likewise. II indicates an identical apparatus which is used as a standard of thickness comparison device. In this case, the coils l2 and H are embodied in the impedance bridge as shown. The coils 24 and 25 in device are inductively associated with the magnets 3! and 34 respectively. suitable adjusting means are provided for each of the gauging devices 29 and 30 similar to the adjusting means shown in Flg. 1 for varying the width of the air gap.

A typical operation of Figs. 2 and 4 is as icllows: A standard of thickness comparison 32 is placed in the gauging device 25 and another standard of thickness comparison 33 of same thickness as 32 is placed in device 30. The air gap of each oi' the devices 29 and 30 is adjusted until the needle 28 of the instrument 21 is at the zero point. The standard of thickness comparison 32 in the gauging device 29 is now removed and the entire device is ready for gauging. The material to be gauged is now placed in the air gap in the device 29 between the magnets 2 and 3 and variations in thickness due to a decrease in the width of the air gap results in a variation in flux compared with the flux resulting from the standard of thickness comparison device 30 and such variations cause a change in the milliampere reading as indlcated by the needle 28 of the instrument 21.

Other means for accomplishing the results of my invention may be used but the above typical examples are illustrative of the broad principles of my invention. My invention is not limited by the apparatus or examples given but is only limited by the following claim.

I claim as my invention:

The method of gauging the thickness oi' material which comprises employing at least two electromagnets spaced from and on opposite sides of said material, predetermining the magnitude of the spacing between the poles oi' the oppositely disposed electromagnets without the presence oi' said material between said poles, adjusting the position of at least one of said electromagnets to give a spacing between their poles equivalent to said predetermined spaclng plus the desired thickness of the material to be gauged, and determining variations from said desired thickness when the material to be gauged is in place between said eelctromagnets by deviations obtained in the flux of the magnetic field as compared with that obtained at said predetermined spacing without the presence of magnetic material in the field.

CHARLES H. ANGELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STA'I'ES PATENTS 

